1. Technical Field
The present invention relates to a light guide device used in a head mounted display or the like mounted on a head and used and a virtual-image display device incorporating the light guide device.
2. Related Art
In recent years, as a virtual-image display device that enables formation and observation of a virtual image like a head mounted display, there have been proposed various virtual-image display devices of a type for guiding video lights received from a display element to the pupils of an observer with a light guide plate.
For example, as a wearable display device that introduces a collimation image or the like into the visual field of an observer, there has been publicly known a wearable display device in which a large number of half mirrors (hereinafter referred to as “HMs” as well) inclined with respect to a principal plane and disposed in parallel to one another are incorporated in a light guide body having a parallel plane plate shape and video lights are reflected by the HMs and provided to the observer (see US 2013/0163089 (Patent Literature 1)). The device makes it possible to observe video lights from an imaging unit as a visible image by reflecting the video lights on the large number of HMs in the light guide body and extracting the video lights while viewing an ambient environment through the light guide body.
In the wearable display device described in Patent Literature 1, see-through view in a short distance is not taken into account. Specifically, when the wearable display device of this type is worn to observe an external object in a short distance, since an array-like HMs are disposed in front of an eye, direct light from the HM, which has transmitted external light, and indirect light reflected by the HM and reflected again by the HM adjacent to the HM are made incident on the eye from the same direction. That is, when the near object is viewed through the light guide body, a ghost is observed because of the indirect light doubly reflected on the HMs. Note that, if it is attempted to increase the transmittance of the HMs to capture more external light, video lights are darkened. On the other hand, if it is attempted to increase the reflectance of the HMs to increase an emitted light amount of the video lights, it is not easy to observe the external environment. For example, if a formation region of the HMs is limited to the front of the eye, the HM formation region is conspicuous in terms of exterior appearance.
Further, in Patent Literature 1, likelihood of occurrence of streak-like unevenness in a visible image in the wearable display device is not described. Specifically, in the case of the wearable display device of this type, since the array-like HMs are disposed in front of the eye, multiple reflection occurs in which lights reflected without being transmitted through the HMs at all and lights transmitted through the HMs once and reflected are made incident on the eye from the same direction. Brightness decreases stepwise according to the number of times of the reflection. Therefore, lights made incident on the eye from respective angle directions have a cyclic luminance distribution corresponding to an array interval in an array direction of the HMs. Since the luminance distribution discontinuously changes according to the angle direction of the lights, vertical streak-like unevenness is observed in the visible image.